Justin C. Shenk

Nucleic acid oxidation in Alzheimer disease

Increasing evidence suggests that oxidative stress is intimately associated with Alzheimer disease pathophysiology. Nucleic acids (nuclear DNA, mitochondrial DNA, and RNA) are one of the several cellular macromolecules damaged by reactive oxygen species, particularly the hydroxyl radical. Because neurons are irreplaceable and survive as long as the organism does, they need elaborate defense mechanisms to ensure their longevity. In Alzheimer disease, however, an accumulation of nucleic acid oxidation is observed, indicating an increased level of oxidative stress and/or a decreased capacity to repair the nucleic acid damage. In this review, we present data supporting the notion that mitochondrial and metal abnormalities are key sources of oxidative stress in Alzheimer disease. Furthermore, we outline the mechanisms of nucleic acid oxidation and repair. Finally, evidence showing the occurrence of nucleic acid oxidation in Alzheimer disease will be discussed.

Alzheimer Disease and the Role of Free Radicals in the Pathogenesis of the Disease

Oxidative stress occurs early in the progression of Alzheimer disease, significantly before the development of the pathologic hallmarks, neurofibrillary tangles and senile plaques. All classes of macromolecules (sugar, lipids, proteins, and nucleic acids) are affected by oxidative stress leading, inevitably, to neuronal dysfunction. Extensive data from the literature support the notion that mitochondrial and metal abnormalities are key sources of oxidative stress in Alzheimer disease. Furthermore, it has been suggested that in the initial stages of the development of Alzheimer disease, amyloid-beta deposition and hyperphosphorylated tau function as compensatory responses to ensure that neuronal cells do not succumb to oxidative damage. However, during the progression of the disease, the antioxidant activity of both agents is either overwhelmed or, according to others, evolves into pro-oxidant activity resulting in the exacerbation of reactive species production.

Neuronal mitochondrial amelioration by feeding acetyl-L-carnitine and lipoic acid to aged rats

Brain function declines with age and is associated with diminishing mitochondrial integrity. The neuronal mitochondrial ultrastructural changes of young (4 months) and old (21 months) F344 rats supplemented with two mitochondrial metabolites, acetyl‐L‐carnitine (ALCAR, 0.2%[wt/vol] in the drinking water) and R‐α‐lipoic acid (LA, 0.1%[wt/wt] in the chow), were analysed using qualitative and quantitative electron microscopy techniques. Two independent morphologists blinded to sample identity examined and scored all electron micrographs. Mitochondria were examined in each micrograph, and each structure was scored according to the degree of injury. Controls displayed an age‐associated significant decrease in the number of intact mitochondria (P = 0.026) as well as an increase in mitochondria with broken cristae (P < 0.001) in the hippocampus as demonstrated by electron microscopic observations. Neuronal mitochondrial damage was associated with damage in vessel wall cells, especially vascular endothelial cells. Dietary supplementation of young and aged animals increased the proliferation of intact mitochondria and reduced the density of mitochondria associated with vacuoles and lipofuscin. Feeding old rats ALCAR and LA significantly reduced the number of severely damaged mitochondria (P = 0.02) and increased the number of intact mitochondria (P < 0.001) in the hippocampus. These results suggest that feeding ALCAR with LA may ameliorate age‐associated mitochondrial ultrastructural decay and are consistent with previous studies showing improved brain function.

Antioxidant Therapy in Alzheimer’s Disease: Theory and Practice

Alzheimer disease treatment has yet to yield a successful therapy that addresses the source of the damage found in brains. Of the varied proposed theories of AD etiology, reactive oxygen species (ROS) generation is cited as a common factor. Efforts to reduce the pathology associated with ROS via antioxidants therefore offer new hope to patients suffering from this devastative disease.

The effect of acetyl-L-carnitine and R-α-lipoic acid treatment in ApoE4 mouse as a model of human Alzheimer's disease

We measured age-dependent effects of human ApoE4 on cerebral blood flow (CBF) using ApoE4 transgenic mice compared to age-matched wild-type (WT) mice by use of [(14)C] iodoantipyrene autoradiography. ApoE4 associated factors reduce CBF gradually to create brain hypoperfusion when compared to WT, and the differences in CBF are greatest as animals age from 6-weeks to 12-months. Transmission electron microscopy with colloidal gold immunocytochemistry showed structural damage in young and aged microvessel endothelium of ApoE4 animals extended to the cytoplasm of perivascular cells, perivascular nerve terminals and hippocampal neurons and glial cells. These abnormalities coexist with mitochondrial structural alteration and mitochondrial DNA overproliferation and/or deletion in all brain cellular compartments. Spatial memory and temporal memory tests showed a trend in improving cognitive function in ApoE4 mice fed selective mitochondrial antioxidants acetyl-l-carnitine and R-alpha-lipoic acid. Our findings indicate that ApoE4 genotype-induced mitochondrial changes and associated structural damage may explain age-dependent pathology seen in AD, indicating potential for novel treatment strategies in the near future.

Atherosclerotic lesions and mitochondria DNA deletions in brain microvessels: Implication in the pathogenesis of Alzheimer’s disease

The pathogenesis that is primarily responsible for Alzheimer’s disease (AD) and cerebrovascular accidents (CVA) appears to involve chronic hypoperfusion. We studied the ultrastructural features of vascular lesions and mitochondria in brain vascular wall cells from human AD biopsy samples and two transgenic mouse models of AD, yeast artificial chromosome (YAC) and C57B6/SJL Tg (+), which overexpress human amyloid beta precursor protein (AβPP). In situ hybridization using probes for normal and 5 kb deleted human and mouse mitochondrial DNA (mtDNA) was performed along with immunocytochemistry using antibodies against the Aβ peptide processed from AβPP, 8-hydroxy-2’-guanosine (8OHG), and cytochrome c oxidase (COX). More amyloid deposition, oxidative stress markers as well as mitochondrial DNA deletions and structural abnormalities were present in the vascular walls of the human AD samples and the AβPP-YAC and C57B6/SJL Tg (+) transgenic mice compared to age-matched controls. Ultrastructural damage in perivascular cells highly correlated with endothelial lesions in all samples. Therefore, pharmacological interventions, directed at correcting the chronic hypoperfusion state, may change the natural course of the development of dementing neurodegeneration.

Hydroxynonenal-generated crosslinking fluorophore accumulation in Alzheimer disease reveals a dichotomy of protein turnover

Lipid peroxidation generates reactive aldehydes, most notably hydroxynonenal (HNE), which covalently bind amino acid residue side chains leading to protein inactivation and insolubility. Specific adducts of lipid peroxidation have been demonstrated in intimate association with the pathological lesions of Alzheimer disease (AD), suggesting that oxidative stress is a major component of AD pathogenesis. Some HNE-protein products result in protein crosslinking through a fluorescent compound similar to lipofuscin, linking lipid peroxidation and the lipofuscin accumulation that commonly occurs in post-mitotic cells such as neurons. In this study, brain tissue from AD and control patients was examined by immunocytochemistry and immunoelectron microscopy for evidence of HNE-crosslinking modifications of the type that should accumulate in the lipofuscin pathway. Strong labeling of granulovacuolar degeneration (GVD) and Hirano bodies was noted but lipofuscin did not contain this specific HNE-fluorophore. These findings directly implicate lipid crosslinking peroxidation products as accumulating not in the lesions or the lipofuscin pathways, but instead in a distinct pathway, GVD, that accumulates cytosolic proteins.

Insights into cerebrovascular complications and Alzheimer disease through the selective loss of GRK2 regulation

•  Introduction •  General features of GRKs •  Expression patterns of GRK2 •  GRK, ET‐1 and Insulin signalling •  GRK studies In AD and CBH •  Conclusions

Stem cell niches as clinical targets: the future of anti-ischemic therapy?

This article provides context for the research presented by Napoli et al., reported in this journal. Treatment strategies that target stem cell niches are promising avenues for stimulating inducible angiogenesis in many vascular diseases, such as diabetes mellitus and atherosclerosis. Here we discuss the study carried out by Napoli and colleagues—an analysis of the effects of parathyroid hormone on the vascular stem cell niche in peripheral ischemia. Napoli et al. demonstrate that parathyroid hormone administered in combination with granulocyte colony-stimulating factor induces angiogenesis in a hindlimb ischemia mouse model. This treatment seems to mobilize and localize endothelial cell progenitors specifically to ischemic vascular cell beds. We explore the mechanisms through which the multiple cells within the vascular niche respond to ischemia. The interaction between parathyroid hormone and granulocyte colony-stimulating factor in humans is also discussed. Further assessment is needed to elucidate the factors involved in migration and differentiation of endothelial cell progenitors in ischemia-damaged tissues.

P4-171: Cerebral hypoperfusion-induced oxidative stress and mitochondrial failure as initiators of aging and Alzheimer's disease pathology

Gjumrakch Aliev, Justin C. Shenk, Kathryn Fischbach, Celia J. Cobb, Gerardo J. Pacheco, Eldar Gasimov, George Perry, Department of Biology, and Electron Microscopy Research Center, University of Texas at San Antonio, San Antonio, TX, USA; Department of Cytology, Histology and Embryology, Azerbaijan Medical University, Baku, Azerbaijan; College of Sciences, University of Texas at San Antonio, San Antonio, TX, USA; Case Western Reserve University, Cleveland, OH, USA. Contact e-mail: gjumrakch.aliev@utsa.edu